Vapor Barriers in Crawlspaces and Basements

We employ vapor barriers when we want to keep water vapor on one side of the barrier and keep it away from whatever is on the other side.  In the St. Louis area, this is most important for crawlspaces and basements as compared to above-grade walls and structures.

For example, we can expect a home built over a dirt floor crawlspace to have a large amount of water vapor in the crawlspace air.  The water vapor comes from the earth and keeps the relative humidity level of the crawlspace air too high.  The combination of wood structural members under the home, air, and moisture make a perfect set of conditions for things like wood rot, mildew and mold.

Vapor Barriers Prevent Damage

In order to prevent bad things, we install a vapor barrier on the floor of the crawlspace.  The barrier keeps water vapor from the earth from getting into the crawlspace air, extends the life of the home, and improves the quality of air that leaks up into the remainder of the home.

In the St. Louis area, one common mistake is to create a vapor barrier in the wrong place when finishing basement walls.  Sometimes homeowners rightly recognize that moisture diffuses from the earth, through the basement walls, and into the basement.  Then they put plastic sheet or some other vapor barrier material in the wrong place and trap moisture where it can cause harm.

The vapor barrier should go directly against the basement wall.  Then all other building materials such as framing, insulation and wall covering should go inside the vapor barrier.  This will keep moisture from the basement walls from reaching the building materials.

If the framing and other materials were placed directly against the wall and then covered with a vapor barrier, the moisture from the basement walls would be trapped between the walls and the vapor barrier.  The building materials would also be trapped inside, with the vapor, and constantly exposed to the damaging effects of moisture.

When working below grade, make sure you have vapor barriers directly against all the surfaces moisture comes from.  Meanwhile, avoid trapping moisture in spaces where it cannot get back out.  As long as you do this, you’ll make the grade.

Contact us today for a free estimate for vapor barrier installation in your crawl space or basement.